The present invention generally relates to an apparatus and a method for positioning gas injectors in a vertical furnace and more particularly, relates to an apparatus and a method for positioning a plurality of gas injectors in a mounting ring in a vertical furnace wherein the gas injectors may be self-positioned without mis-installation.
In connection with processes used to manufacture semiconductor devices, such as integrated circuits, numerous process steps are carried out in a controlled environment at elevated temperatures. Such processes includes oxidation, diffusion, chemical vapor deposition and annealing. In order to realize elevated processing temperatures, semiconductor wafers are processed in an evacuated chamber, typically in a form of a quartz tube which is housed within a semiconductor furnace.
The most common type of semiconductor furnace is of the so-called xe2x80x9chot wall xe2x80x9d electric type which facilitates batch processing of semiconductor wafers. Furthermore, hot wall electric furnaces exhibit excellent temperature stability and precise temperature control. Modern hot wall diffusion furnaces are capable of controlling temperatures over the range of 300xc2x0-1200xc2x0 C. to an accuracy of 0.5xc2x0 or xe2x88x920.5xc2x0 C. Hot wall furnaces were initially designed as horizontal diffusion furnaces, however, more recently, vertical furnaces have gained favor because they present a number of advantages over their horizontal predecessors. These advantages include: elimination of cantilever or soft-landing since the wafers are held in a quartz boat which does not touch the process tube walls; wafers can be loaded and unloaded automatically; and, the clean room footprint of the system is somewhat smaller than that of the conventional horizontal configuration.
Vertical semiconductor furnaces of the type mentioned above employ a quartz tube which typically has a polysilicon coating when used for a deposition or annealing process. The polysilicon deposition reduces the power loss due to quartz reflection or radiation, and reduces the degradation of a boat occasioned by wet etching. Because semiconductor furnaces are subjected to high rates of usage and their components are exposed to harsh operating environments, periodic maintenance must be performed on various furnace components, including the quartz tube assembly.
In a vertical furnace, a plurality of gas injectors for flowing into the furnace a variety of process gases is also provided. The gas injectors are normally formed of quartz tubes and are positioned in a mounting ring at a bottom of the furnace. The gas injectors are normally formed in a xe2x80x9cLxe2x80x9d shape such that the horizontal portion of the xe2x80x9cLxe2x80x9d sits in a slot opening provided in the mounting ring while the vertical portion of the xe2x80x9cLxe2x80x9d stands perpendicularly to the mounting ring with a number of nozzle openings provided in the quartz tube for flowing a process gas therethrough. Several different process gases may be required for a single process. For instance, in a chemical vapor deposition process for forming silicon oxide, at least three gas injectors for feeding the three different gases are provided in the vertical furnace. During SiO2 deposition, a first gas injector may be used for feeding silane gas into the chamber cavity, a second gas injector may be used for feeding N2O gas into the chamber cavity, while a third gas injector may be used to feed a carrier or a dilution gas of N2 into the chamber cavity.
In a typical chemical vapor deposition process conducted in a vertical furnace, as many as 172 wafers may be stacked in a wafer boat and positioned in the chamber cavity. In order to accommodate a large wafer boat that carries as many as 172 wafers, a substantially tall furnace tube must be utilized. For instance, a vertical furnace tube as long as 150 cm may be necessary to allow the processing of a large number of wafers. During the furnace process, the positioning of the various gas injectors in the furnace cavity is therefore important not only from a quality point-of-view, but also from a process repeatability point-of-view. In order to carry out a consistent deposition process, the position of each gas injector for the particular process gas must be exactly the same during each batch of wafer processing. For instance, in SiO2 deposition, the length of the plurality of gas injectors may range between about 60 cm and about 150 cm. A repeatable process can only be achieved by locating the plurality of gas injectors at exactly the same location each time the process is repeated on a different batch of wafers. The positioning, or the ability to self-positioning the plurality of gas injectors in a vertical furnace is therefore very important.
It is therefore an object of the present invention to provide a vertical furnace that is equipped with a plurality of gas injectors for processing wafers in the furnace cavity that does not have the drawbacks or shortcomings of the conventional vertical furnace.
It is another object of the present invention to provide a vertical furnace that is equipped with self-positioning gas injectors for processing wafers that is capable of producing repeatable results.
It is a further object of the present invention to provide a vertical furnace that is equipped with self-positioning gas injectors for processing wafers wherein a plurality of quartz gas injectors in xe2x80x9cLxe2x80x9d configuration is utilized.
It is another further object of the present invention to provide a vertical furnace that is equipped with self-positioning gas injectors for processing wafers wherein a plurality of quartz gas injectors in xe2x80x9cLxe2x80x9d configuration each equipped with a stopper mounted on a horizontal portion of the injector is utilized.
It is still another object of the present invention to provide a vertical furnace that is equipped with self-positioning gas injectors for processing wafers wherein a mounting ring which has a plurality of slot openings each with a different dimension for mounting the plurality of gas injectors is provided.
It is yet another object of the present invention to provide a vertical furnace that is equipped with self-positioning gas injectors for processing wafers wherein a plurality of slot openings of varying dimensions is provided in a mounting ring for the self-positioning of a plurality of gas injectors each equipped with a stopper mounted on the injector at a different location.
It is still another further object of the present invention to provide a method for mounting a plurality of gas injectors in a vertical furnace for processing wafers by first mounting a stopper to the plurality of gas injectors at a different position for each process gas such that the gas injectors are installed in the mounting ring at the same location repeatedly.
In accordance with the present invention, an apparatus and a method for positioning gas injectors in a vertical furnace with repeatable results such that the same gas injector is always installed at the same location are provided.
In a preferred embodiment, a vertical furnace that is equipped with self-positioning gas injectors for processing wafers is provided which includes a cylindrical-shaped tube that has a sealed top and an open bottom, the open bottom is sealable by an end cap; a cavity formed inside the cylindrical-shaped tube that has a size sufficient for a wafer carrier to be positioned therein; a mounting ring for positioning inside the cavity juxtaposed to the open bottom, the mounting ring has a substantially rectangular cross-section, a width in the radial direction, a thickness in the vertical direction, and a plurality of slot openings each opens to an outer periphery of the ring and each has a different depth cut into the width of the ring; and a plurality of gas injectors each formed in an xe2x80x9cLxe2x80x9d shape with a vertical portion and a horizontal portion in fluid communication with each, each of the horizontal portions has an inlet end and is provided with a stopper mounted on a bottom surface at a different location for each injector when measured from the inlet end of the horizontal portion such that when the plurality of gas injectors are positioned on top of the mounting ring with each of the nozzle stoppers engaging a corresponding one of the plurality of slot openings, the horizontal portions of the plurality of gas injectors extend into the cavity of the cylindrical-shaped tube in the radial direction at a substantially equal distance as measured from an inner surface of the cylindrical-shaped tube.
The vertical furnace that is equipped with self-positioning gas injectors for processing wafers may further include an inner tube positioned inside the cylindrical-shaped tube for defining the cavity. The cylindrical-shaped tube may further include a plurality of apertures adapted for the inlet ends of the plurality of gas injectors to penetrate therethrough. The inlet ends of the plurality of gas injectors may each be provided with an O-ring for sealingly engaging a gas supply conduit. The cavity may be sufficiently large for a wafer boat that carries at least 172 wafers to be positioned therein. The cylindrical-shaped tube may be fabricated of a substantially transparent, high temperature resistant ceramic material; the cylindrical-shaped tube and the plurality of gas injectors may be fabricated of quartz. The mounting ring may be fabricated of a high temperature and corrosion-resistant material, such as stainless steel. The vertical portions of the plurality of gas injectors may further include at least one aperture as a gas outlet. The vertical portions of the plurality of gas injectors may each have a length between about 50 cm and about 150 cm. The stoppers may be mounted as on the plurality of gas injectors each being formed to a length of at least 5 mm, a height of at least 5 mm and a thickness of at least 5 mm. The stoppers may be formed of quartz and are fused to the horizontal portions of the plurality of gas injectors. The horizontal portions of the plurality of gas injectors may have the same length of at least 40 mm.
The present invention is further directed to a method for mounting a plurality of gas injectors in a vertical furnace for processing wafers which may be carried out by the operating steps of first providing a furnace body of a cylindrical-shaped tube that has a sealed top and an open bottom, the open bottom may be sealable by an end cap, the furnace body may have a cavity formed therein having a size sufficient for a wafer carrier to be positioned therein, the furnace body may further have a mounting ring positioned inside the cavity juxtaposed to the open bottom, the mounting ring may have a substantially rectangular cross-section, section, a width in the radial direction, a thickness in the vertical direction and a plurality of slot openings each opens to an outer periphery of the ring and each has a different depth cut into the width of the ring; then providing a plurality of gas injectors in tubular shape each formed in a xe2x80x9cLxe2x80x9d configuration that has a vertical portion and a horizontal portion in fluid communication with each other, each of the horizontal portions may have an inlet and are provided with a stopper mounted on a bottom surface at a location different than the other gas injectors when measured from the inlet end of the horizontal portion; and positioning the plurality of gas injectors on top of the mounting ring by engaging each of the stoppers on the gas injectors to a corresponding one of the plurality of slot openings on the mounting ring such that the horizontal portions of the plurality of gas injectors extend into the cavity of the cylindrical-shaped tube in a radial direction at a substantially equal distance as measured from an inner surface of the cylindrical-shaped tube.
The method for mounting a plurality of gas injectors in a vertical furnace for processing wafers may further include the step of penetrating the inlet ends of the plurality of gas injectors through a plurality of apertures in the furnace body for connecting to a plurality of gas supplies. The method may further include the step of mounting onto each of the inlet ends of the plurality of gas injectors an O-ring for sealingly engaging a gas supply conduit. The method may further include the step of preventing the vertical portions of the plurality of gas injectors from tilting away from a vertical position by engaging the stoppers on the gas injectors to the slot openings in the mounting ring. The method may further include the step of fabricating the cylindrical-shaped tube and the plurality of gas injectors in quartz, or the step of fabricating the mounting ring in a high temperature and corrosion-resistant material such as stainless steel. The method may further include the step of fabricating the vertical portions of the plurality of gas injectors with at least one aperture for gas outlet.